This invention is related to U.S. Pat. No. 5,420,953 assigned to the assignee of the present invention.
The use of monocrystalline materials has enabled the passive alignment of optical devices to optical fiber for optical communication. The use of such materials to replace the requirements for active device alignment has great potential to effect the low cost, large production of optical links that have application to Fiber to the Home (FTTH) and Fiber to the Office (FTTO). Accordingly, the recent past has seen a great deal of interest and inventive activity in the development of passive alignment based on the use of monocrystalline materials. A common material for such use is monocrystalline silicon, as its crystalline properties are well known in the art. In U.S. Pat. No. 4,210,923 to North, et al., typical techniques for etching silicon is disclosed, and the disclosure of the North, et al. patent is specifically incorporated herein by reference.
One of the preferred set of devices in the optical communication technology is the surface emitting and detecting device. To this end, the use of devices such as Vertical Cavity Surface Emitting Lasers (VCSELS) and photodetectors (such as PIN photodiodes) that have the photosensitive surface to receive or emit light on the top surface has required a great deal of modification to effect the alignment of the device to an optical fiber. In general, to effect the alignment between the device and the fiber using a silicon optical bench, it is required to have the device on a different plane that the fiber, with the light being communicated therebetween by a reflective surface. Examples of such techniques are found for example in U.S. Pat. Nos. 5,073,003 and 4,904,036, to Clark and Blonder, respectively, the disclosures of which are specifically incorporated herein by reference. While such technology has its merits in allowing passive alignment to some extent, it is nonetheless required that the device be actively aligned into position so that light is properly reflected by the reflective surface. Furthermore, the use of a reflective surface decreases coupling efficiency, since there are intrinsic losses incurred at each optical surface through dispersive effects. Accordingly, a more efficient system would allow for in-line coupling between the fiber and the device.
U.S. Pat. No. 5,179,609 to Blonder, et al. discloses an example of the use of silicon waferboard technology to effect the coupling between the device and the fiber in a co-linear fashion. The disclosure of this patent is specifically incorporated herein by reference. This reference makes use of two pieces of monocrystalline material as mounting members that have etched therein detents in complimentary locations on each of the pieces of the mounting members. These detents receive microspheres to effect the alignment of the mounting members to effect the coupling of the device to the fiber. While the reference does disclose the use of other types of alignment fiducials, there are two substantive drawbacks to the invention disclosed in this reference. To effect alignment, there is required a separate member for holding the device to be coupled to the fiber, and another member to hold the optical fiber. Furthermore, the alignment fiducials are separated piece parts that are placed between the waferboard holding the fiber and the waferboard holding the device.
As can be readily appreciated from a study of the disclosure of this reference, the alignment fiducials are an additional processing step requiring additional parts to effect alignment. Furthermore, the alignment fiducials of this reference are a potential source of misplacement and thereby misalignment of the members. Accordingly, what is needed is an apparatus that allows for direct attachment of the optical fiber and the device to a single alignment member. Furthermore, what is needed is an apparatus that enables passive alignment via alignment pedestals and standoffs that are integrally formed from and on the single alignment member. The alignment therebetween is thereby made simply and effectively at a lower cost in manufacture.